Hemoglobins show a very great range in their functional properties and hemoglobin systems often show striking adaptations to environmental pressures. In the freshwater trout, and in a number of marine fish, functionally diverse hemoglobin components are present. Some hemoglobin components show large pH and cofactor effects in oxygen binding. The properties of these components may permit the fish to exquisitely control the delivery of oxygen to specialized organs as diverse as the swimbladder and the retina. The exaggerated effects of pH and anions on the oxygen binding properties of these proteins makes them useful as probes of allosteric control mechanisms. Other hemoglobin components show no pH dependence in oxygen binding and are essentially unaffected by variations in temperature or organic phosphate concentration. These may serve as physiological "back-ups" that allow for oxygen uptake and delivery in spite of environmental or physiological perturbations. Exploration of structure-function relationships in these unusual hemoglobins is of considerable interest since cooperative interactions are divorced from pH and anion effects. Studies on the primary structures of the two major trout hemoglobin components will be continued and sequence analysis of the single hemoglobin of a marine teleost will be initiated. Immunological techniques will be utilized to estimate the relatedness of both marine and freshwater fish hemoglobins. Properties of isolated chains of fish hemoglobins will be analyzed and hybrid (fish-human) tetramers will be characterized. Enzymatically modified and cross-linked hemoglobins will also be examined. Functional analysis will include comparative studies of oxygen binding by red cells, hemolysates and purified fish hemoglobins and detailed analysis of oxygen binding curves obtained with an Imai apparatus. Ligand binding mechanisms will be explored via rapid-mixing and flash photolysis techniques in conjunction with steady-state photochemical experiments. Complementary physiological experiments will investigate the adaptive significance of multiple hemoglobin types and "fetal" hemoglobins in fish and the allosteric interaction of fish hemoglobins with carbon dioxide.